1. Field
Embodiments described herein relate to an electrically data-rewritable nonvolatile semiconductor memory device.
2. Description of the Related Art
In recent years, many semiconductor memory devices are proposed in which memory cells are disposed three-dimensionally in order to increase a degree of integration of memory.
For example, one conventional semiconductor memory device in which memory cells are disposed three-dimensionally uses a transistor with a cylindrical column type structure. The transistor with the cylindrical column type structure includes a conductive layer stacked in multiple layers and configured to form a pillar-shaped columnar semiconductor layer, a memory gate insulating layer, and a gate electrode. The columnar semiconductor layer functions as a channel (body) portion of the transistor. The memory gate insulating layer is formed in a periphery of the columnar semiconductor layer and configured to enable storage of a charge. The conductive layer is formed around the columnar semiconductor layer with the memory gate insulating layer interposed therebetween. Such a three-dimensional structure enables increased capacity to be achieved not through miniaturization but through multilayering, and a manufacturing process may be performed using a technology that is an extension of conventional technology.
Through manufacturing processes for the above-described transistor with the cylindrical column type structure, an upper wiring, a lower wiring, and a plug layer used in a control circuit of the transistor are formed. The upper wiring is provided in an upper portion of the conductive layer, the lower wiring is provided in a lower portion of the conductive layer, and the plug layer is formed extending in a perpendicular direction so as to connect the upper wiring and the lower wiring.
Further, the plug layer is formed as below. That is, first, a penetrating hole is formed penetrating the conductive layer in a portion of a region. Next, an interlayer insulating layer is formed filing the penetrating hole. Then, a plurality of holes are formed penetrating the interlayer insulating layer, and a plug layer formed within each of the holes. However, when the interlayer insulating layer is formed, a void is formed in the interlayer insulating layer if coverage of the filling material of the interlayer insulating layer is insufficient. A plurality of penetrating holes subsequently formed therein may be electrically connected to each other via the void. That is, a plurality of plug layers are short-circuited via the void, and stability of operation in the nonvolatile semiconductor memory device is impaired.